1. Field of the Invention
The present invention relates generally to the control of a hybrid electric vehicle, and more particularly to a method for controlling activation of a power source of a hybrid electric vehicle.
2. Background Art
Hybrid electric vehicles have been proposed that turn off an engine and use battery power to propel the vehicle at low speeds (e.g., less than 5 mph or from a complete stop). These vehicles emphasize the importance of not operating the engine at low speeds to conserve fuel. However, such vehicles may have insufficient electrical power or motor torque to simultaneously propel the vehicle and start the engine. As a result, there may be delayed engine starts, sluggish vehicle acceleration, and rapid depletion of battery charge. The use of higher capacity batteries to address these issues is undesirable since such batteries have increased cost, size, and/or weight.